Electronic devices, such as electronic book readers (“eBook reader devices”), cellular telephones, portable media players, desktop computers, laptops, tablet computers, netbooks, personal digital assistants, and the like, rely on electrical power to function.
Within these electronic devices, several components utilize significant amounts of power during operation, including the processor(s) and peripheral devices. These peripheral devices include external memory interfaces (EMIs), Universal Serial Bus (USB) controllers, image processing units (IPUs), and so forth. These peripheral devices may reside on the same “chip” or die as the processor and/or may reside on another die.
A peripheral device that is not actively in use but is idling continues to consume significant quantities of power. This idling wastes energy and increases the amount of heat dissipated by the electronic device. Conversely, reducing power consumption increases the usable time for a portable device operating from a battery. Reducing power consumption also reduces the heat dissipated by the electronic device, allowing it to operate at a cooler temperature and thus increasing the life of the equipment and simplifying cooling design.
Various schemes have been put forth to reduce power consumption in portable consumer devices by placing the processor and the peripherals into lower power modes. Typically, this involves turning off unused portions of the circuit and/or reducing a clock speed of the microprocessor.
However, these techniques often introduce undesirable latencies to execution of commands upon resumption of normal activity, particularly with regard to providing an updated image to a display.